RAF Association - The website of the RAF Association - there appears to no longer be an assocuiation specific to Bomber Command..
Bob Baxter's Bomber Command - Bob Baxter maintains all sorts of information on losses etc. for Bomber Command. His onward links also open a world of information. Bob himself is happy to help with detail and recommended further reading on the mission where KM-T was shot down which has proven highly interesting.
Royal Air Force (RAF) Bomber Command 1939-1945 - Rob Davis' site which contains excellent information on how Bomber Command worked in WWII and loads of interesting statistics. The page Researching an Operational History gives useful guidelines on how and where to hunt down more information and Rob is also happy to help you with any information he already holds in his extensive database.
Aircrew Remembered - An excellent site, aiming to remember those who served within the aviation story of our past. The site includes a number of searchable databases of crew losses here, although these have various levels of completeness.
The Commonwealth War Graves Commission - The place to look for information on the men that fell during the two world wars with an excellent search facility.
The Australian War Memorial - Remembering Australians who lost their lives fighting in the two world wars including many in the RAAF.
The WWII Nominal Roll - The archive of the Australians who served with Commonwealth forces during WWII.
The Canadian Virtual War Memorial - Remembering Canadians who lost their lives fighting in the two world wars including many in the RCAF.
Air of Authority - A history of RAF organisation, a goldmine of useful information on the various units, commands and ranks of the RAF since the days of the RFC to modern times by Malcolm Barrass.
The Nachtjagd Claims Database - A searchable list of the aircraft claims made by the German Night Fighter pilots throughout WWII (now defunct). Some of the lists are still downloadable as Word or PDF files from Tony Wood's site. The locations in the database can be interpreted using the Jaegergradnetzkarte (Fighter Grid Map) at the JG26 site.
The Lancaster Archive - Larry Wright's site giving lots of useful Lancaster related information.
RAF Commands - A forum style discussion list on all things RAF between 1939 and 1945 moderated by Ross McNeill. Someone there will have the answer to just about any question.
LostAircraft.com - A website is dedicated to the pilot and aircrew casualties of World War II. It is intended to be an information sharing platform for historians, genealogists and next-of-kin, who can publish and gain access to relevant information in the form of original documents and photographs, excepts and quotes from books and newspapers, eye-witness reports and links to other websites.
WWII Escape and Evasion Information Exchange - Part of the Conscript Heroes website, with information on evaders and escapers.
The National Archives - The website of the UK National Archives at Kew, giving opening times and listing what records they hold and information about how to go about gaining access at Kew as well as offering a copying service for documents held. Hunting out the right documents given the referencing system can be confusing though!
NARA - The US equivalent of the National Archives. Many documents are available online here.
The Airfield Research Group - The site of the ARG, who are a charitable organisation dedicated to research on airfield history of all types. The forum (linked) is full of interesting discussions and pictures of airfields past and present all around the globe.
Facebook - In addition there are a number of pages on Facebook inhabited by people willing and able to assist in finding information on aircrew. The prime ones I use is the Bomber Command Research Page and the Wartime RAF/army personnel research group. There are also a number of individual Squadron and Aircraft type interest groups who can often assist with research. There is also a 44 (Rhodesia) Squadron page. Use the search function on Facebook.
"I salute your father and others of the crew, whose props may have stopped turning, but who are not forgotten." Rob Davis